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The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
  • 2017-03-09 08:05:43
  • Article ID: 670861

Cracking the Mystery of Perfect Efficiency: Investigating Superconductors

From the turn of the last century to today, scientists have explored why superconductors never lose current.

  • Credit: Image is taken from the Report of the Basic Energy Sciences Workshop on Superconductivity, May 8-11, 2006

    This figure shows how electrons pair up to cause superconductivity. Instead of traveling independently, the electrons couple into pairs that flow through metal without resistance.

  • Credit: Image is taken from the Report of the Basic Energy Sciences Workshop on Superconductivity, May 8-11, 2006

    In copper and iron-based superconductors, the spins on adjacent sites have north and south poles that alternate directions. Scientists think that the ordering of these magnetic poles may affect the electrons' interactions.

In 1911, physicist Heike Kamerlingh Onnes aimed to lower mercury’s temperature to as close to absolute zero as possible. He hoped to win a disagreement with Lord Kelvin, who thought metals would stop conducting electricity altogether at extremely low temperatures. Carefully manipulating a set of glass tubes, Kamerlingh Onnes and his team lowered the mercury’s temperature to 3 K (-454 F). Suddenly, the mercury conducted electricity with zero resistance. Kamerlingh Onnes had just discovered superconductivity.

This single finding led to a worldwide investigation that’s spanned a century. While it resolved one scientific debate, it created many more. The Department of Energy’s Office of Science and its predecessors have spent decades supporting scientists investigating the mystery of why superconductivity occurs under a variety of circumstances.

The answer to this question holds major opportunities for scientific and technological development. About six percent of all electricity distributed in the U.S. is lost in transmission and distribution. Because superconductors don’t lose current as they conduct electricity, they could enable ultra-efficient power grids and incredibly fast computer chips. Winding them into coils produces magnetic fields that could be used for highly-efficient generators and high-speed magnetic levitation trains. Unfortunately, technical challenges with both traditional and “high temperature” superconductors restrict their use.

“To the extent that Tesla and Edison introducing the use of electricity revolutionized our society, ambient superconductivity would revolutionize it once again,” said J.C. Séamus Davis, a physicist who works with the Center for Emergent Superconductivity, a DOE Energy Frontier Research Center.

The How and Why of Superconductivity

Kamerlingh Onnes’ discovery set off a flurry of activity. Despite his grand visions, most of what scientists found only reinforced superconductors’ limitations.

One of the first big breakthroughs came nearly half a century after Kamerlingh Onnes’ initial finding. While most researchers thought superconductivity and magnetism couldn’t co-exist, Alexei A. Abrikosov proposed “Type II” superconductors that can tolerate magnetic fields in 1952. Abrikosov continued his research at DOE’s Argonne National Laboratory (ANL) and later won the Nobel Prize in Physics for his contributions.

The next big leap came in 1957, when John Bardeen, Leon Cooper, and John Robert Schrieffer proposed the first theory of why superconductivity occurs. Their theory, made possible by the support of DOE’s predecessor, the Atomic Energy Commission, also won them the Nobel Prize in physics.

Their theory contrasts how some metals work under normal conditions with how they act at extremely low temperatures. Normally, atoms are packed together in metals, forming regular lattices. Similar to the spokes and rods of Tinkertoys, the metals’ positively charged ions are bonded together. In contrast, negatively charged free electrons (electrons not tied to an ion) move independently through the lattice.

But at extremely low temperatures, the relationship between the electrons and the surrounding lattice changes. A common view is that the electrons’ negative charges weakly attract positive ions. Like someone tugging the middle of a rubber band, this weak attraction slightly pulls positive ions out of place in the lattice. Even though the original electron has already passed by, the now displaced positive ions then slightly attract other electrons. At near absolute zero, attraction from the positive ions causes electrons to follow the path of the ones in front of them. Instead of travelling independently, they couple into pairs. These pairs flow easily through metal without resistance, causing superconductivity.

Discovering All-New Superconductors

Unfortunately, all of the superconductors that scientists had found only functioned near absolute zero, the coldest theoretically possible temperature.

But in 1986, Georg Bednorz and K. Alex Müller at IBM discovered copper-based materials that become superconducting at 35 K (-396 F). Other scientists boosted these materials’ superconducting temperature to close to 150 K (-190 F), enabling researchers to use fairly common liquid nitrogen to cool them.

In the last decade, researchers in Japan and Germany discovered two more categories of high-temperature superconductors. Iron-based superconductors exist in similar conditions to copper-based ones, while hydrogen-based ones only exist at pressures more than a million times that of Earth’s atmosphere.

But interactions between the electron pairs and ions in the metal lattice that Bardeen, Cooper, and Schrieffer described couldn’t explain what was happening in copper and iron-based high temperature superconductors.

“We were thrown into a quandary,” said Peter Johnson, a physicist at Brookhaven National Laboratory (BNL) and director of its Center for Emergent Superconductivity. “These new materials challenged all of our existing ideas on where to look for new superconductors.”

In addition to being scientifically intriguing, this conundrum opened up a new realm of potential applications. Unfortunately, industry can only use “high-temperature” superconductors are for highly specialized applications. They are still too complex and expensive to use in everyday situations. However, figuring out what makes them different from traditional ones may be essential to developing superconductors that work at room temperature. Because they wouldn’t require cooling equipment and could be easier to work with, room temperature superconductors could be cheaper and more practical than those available today.

A Shared Characteristic

Several sets of experiments supported by the Office of Science are getting us closer to finding out what, if anything, high-temperature superconductors have in common. Evidence suggests that magnetic interactions between electrons may be essential to why high-temperature superconductivity occurs.

All electrons have a spin, creating two magnetic poles. As a result, electrons can act like tiny refrigerator magnets. Under normal conditions, these poles aren’t oriented in a particular way and don’t interact. However, copper and iron-based superconductors are different. In these materials, the spins on adjacent iron sites have north and south poles that alternate directions – oriented north, south, north, south and so on.

One project supported by the Center for Emergent Superconductivity examined how the ordering of these magnetic poles affected their interactions. Scientists theorized that because magnetic poles were already pointing in opposite directions, it would be easier than usual for electrons to pair up. To test this theory, they correlated both the strength of bonds between electrons (the strength of the electron pairs) and the direction of their magnetism. With this technique, they provided significant experimental evidence of the relationship between superconductivity and magnetic interactions.

Other experiments at a number of DOE’s national laboratories have further reinforced this theory. These observations met scientists’ expectations of what should occur if superconductivity and magnetism are connected.

Researchers at ANL observed an iron-based superconductor go through multiple phases before reaching a superconducting state. As scientists cooled the material, iron atoms went from a square structure to a rectangular one and then back to a square one. Along the way, there was a major change in the electrons’ magnetic poles. While they were originally random, they assumed a specific order right before reaching superconductivity.

At DOE’s Ames Laboratory, researchers found that adding or removing electrons from an iron-based superconducting material changed the direction in which electricity flowed more easily. Researchers at BNL observed that superconductivity and magnetism not only co-exist, but actually fluctuate together in a regular pattern.

Unfortunately, electron interactions’ complex nature makes it difficult to pinpoint exactly what role they play in superconductivity.

Research at BNL found that as scientists cooled an iron-based material, the electron spins’ directions and their relationship with each other changed rapidly. The electrons swapped partners right before the material became superconducting. Similarly, research at ANL has showed that electrons in iron-based superconductors produce “waves” of magnetism. Because some of the magnetic waves cancel each other out, only half of the atoms demonstrate magnetism at any one time.

These findings are providing new insight into why superconductors behave the way they do. Research has answered many questions about them, only to bring up new ones. While laboratories have come a long way from Kamerlingh Onnes’ hand-blown equipment, scientists continue to debate many aspects of these unique materials.

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What's On Your Skin? Archaea, That's What

It turns out your skin is crawling with single-celled microorganisms - (break)and they're not just bacteria. A study by the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and the Medical University of Graz has found that the skin microbiome also contains archaea, a type of extreme-loving microbe, and that the amount of it varies with age.

Magnetic Particles that Flock Like Birds

Tracking movements of individual particles provides understanding of collective motions, synchronization and self-assembly.

'On Your Mark, Get Set' Neutrons Run Enzyme's Reactivity for Better Biofuel Production

Producing biofuels like ethanol from plant materials requires various enzymes to break down the cellulosic fibers. Researchers from ORNL and NC State used neutrons to identify the specifics of an enzyme-catalyzed reaction that could significantly reduce the total amount of enzymes used, improving production processes and lowering costs.

Magnetic Curve Balls

A twisted array of atomic magnets were driven to move in a curved path, a needed level of control for use in future memory devices.

New "Gold Standard" for Flexible Electronics

Simple, economical process makes large-diameter, high-performance, thin, transparent, and conductive foils for bendable LEDs and more.

Microbe Mystery Solved: What Happened to the Deepwater Horizon Oil Plume

The Deepwater Horizon oil spill in the Gulf of Mexico in 2010 is one of the most studied spills in history, yet scientists haven't agreed on the role of microbes in eating up the oil. Now a research team at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has identified all of the principal oil-degrading bacteria as well as their mechanisms for chewing up the many different components that make up the released crude oil.

New Class of 'Soft' Semiconductors Could Transform HD Displays

New research by Berkeley Lab scientists could help usher in a new generation of high-definition displays, optoelectronic devices, photodetectors, and more. They have shown that a class of "soft" semiconductors can be used to emit multiple, bright colors from a single nanowire at resolutions as small as 500 nanometers. The work could challenge quantum dot displays that rely upon traditional semiconductor nanocrystals to emit light.

Could This Strategy Bring High-Speed Communications to the Deep Sea?

A new strategy for sending acoustic waves through water could potentially open up the world of high-speed communications to divers, marine research vessels, remote ocean monitors, deep sea robots, and submarines. By taking advantage of the dynamic rotation generated as the acoustic wave travels, also known as its orbital angular momentum, Berkeley Lab researchers were able to pack more channels onto a single frequency, effectively increasing the amount of information capable of being transmitted.

2-D Material's Traits Could Send Electronics R&D Spinning in New Directions

Researchers created an atomically thin material at Berkeley Lab and used X-rays to measure its exotic and durable properties that make it a promising candidate for a budding branch of electronics known as "spintronics."

Manipulating Earth-Abundant Materials to Harness the Sun's Energy

New material based on common iron ore can help turn intermittent sunlight and water into long-lasting fuel.


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Yi Cui Named Blavatnik National Laureate

Pioneering nanoscientist Yi Cui, professor of materials science and engineering at Stanford University and of photon science at the Department of Energy's SLAC National Accelerator Laboratory, has been named a 2017 Blavatnik National Laureate. The $250,000 award recognizes the most promising researchers age 42 and younger at top U.S. academic and research institutions.

Protein Data Takes Significant Step Forward in Medicine

Scientists at the Pacific Northwest National Laboratory and Oregon Health & Science University are part of a nationwide effort to learn more about the role of proteins in cancer biology and to use that information to benefit cancer patients.

The Electrochemical Society and Toyota North America Announce 2017-2018 Fellowship Winners for Projects in Green Energy Technology

The ECS Toyota Young Investigator Fellowship Selection Committee has chosen three winners who will receive $50,000 fellowship awards each for projects in green energy technology. The awardees are Dr. Ahmet Kusoglu, Lawrence Berkeley National Laboratory; Professor Julie Renner, Case Western Reserve University; and Professor Shuhui Sun, Institut National de la Rechersche Scientifique (INRS).

Chicago Quantum Exchange to Create Technologically Transformative Ecosystem

The University of Chicago is collaborating with the U.S. Department of Energy's Argonne National Laboratory and Fermi National Accelerator Laboratory to launch an intellectual hub for advancing academic, industrial and governmental efforts in the science and engineering of quantum information.

Department of Energy Awards Six Research Contracts Totaling $258 Million to Accelerate U.S. Supercomputing Technology

Today U.S. Secretary of Energy Rick Perry announced that six leading U.S. technology companies will receive funding from the Department of Energy's Exascale Computing Project (ECP) as part of its new PathForward program, accelerating the research necessary to deploy the nation's first exascale supercomputers.

Cynthia Jenks Named Director of Argonne's Chemical Sciences and Engineering Division

Argonne has named Cynthia Jenks the next director of the laboratory's Chemical Sciences and Engineering Division. Jenks currently serves as the assistant director for scientific planning and the director of the Chemical and Biological Sciences Division at Ames Laboratory.

Argonne-Developed Technology for Producing Graphene Wins TechConnect National Innovation Award

A method that significantly cuts the time and cost needed to grow graphene has won a 2017 TechConnect National Innovation Award. This is the second year in a row that a team at Argonne's Center for Nanoscale Materials has received this award.

Honeywell UOP and Argonne Seek Research Collaborations in Catalysis Under Technologist in Residence Program

Researchers at Argonne are collaborating with Honeywell UOP scientists to explore innovative energy and chemicals production.

Follow the Fantastic Voyage of the ICARUS Neutrino Detector

The ICARUS neutrino detector, born at Gran Sasso National Lab in Italy and refurbished at CERN, will make its way across the sea to Fermilab this summer. Follow along using an interactive map online.

JSA Awards Graduate Fellowships for Research at Jefferson Lab

Jefferson Sciences Associates announced today the award of eight JSA/Jefferson Lab graduate fellowships. The doctoral students will use the fellowships to support their advanced studies at their universities and conduct research at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) - a U.S. Department of Energy nuclear physics laboratory managed and operated by JSA, a joint venture between SURA and PAE Applied Technologies.


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Magnetic Particles that Flock Like Birds

Tracking movements of individual particles provides understanding of collective motions, synchronization and self-assembly.

Graphene Ribbons Result in 100-Fold Increase in Gold Catalyst's Performance

Bottom-up synthesis of tunable carbon nanoribbons provides a new route to enhance industrial, automotive reactions.

Breaking the Rules to Make Electricity from Waste Heat

More atomic bonds is the key for performance in a newly discovered family of cage-structured compounds.

Magnetic Curve Balls

A twisted array of atomic magnets were driven to move in a curved path, a needed level of control for use in future memory devices.

New "Gold Standard" for Flexible Electronics

Simple, economical process makes large-diameter, high-performance, thin, transparent, and conductive foils for bendable LEDs and more.

New Class of Porous Materials Better Separates Carbon Dioxide from Other Gases

Enhanced stability in the presence of water could help reduce smokestack emissions of greenhouse gases.

Manipulating Earth-Abundant Materials to Harness the Sun's Energy

New material based on common iron ore can help turn intermittent sunlight and water into long-lasting fuel.

Oxygen: The Jekyll and Hyde of Biofuels

Scientists are devising ways to protect plants, biofuels and, ultimately, the atmosphere itself from damage caused by an element that sustains life on earth.

The Rise of Giant Viruses

Research reveals that giant viruses acquire genes piecemeal from others, with implications for bioenergy production and environmental cleanup.

Grasses: The Secrets Behind Their Success

Researchers find a grass gene affecting how plants manage water and carbon dioxide that could be useful to growing biofuel crops on marginal land.


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